assertThrows(
        NullPointerException.class,
        () -> ImmutableSetMultimap.copyOf((Multimap<String, Integer>) input));
  }

  public void testToImmutableSetMultimap() {
    Collector<Entry<String, Integer>, ?, ImmutableSetMultimap<String, Integer>> collector =
        toImmutableSetMultimap(Entry::getKey, Entry::getValue);